Wipe it with alcohol. One of the easiest ways to prevent grout from getting dirty is to clean it often with something that will prevent mold and mildew from forming in the first place. One such substance is alcohol. Once a week, wipe the grout down with isopropyl (rubbing) alcohol using a clean cloth.
Spray it with a mold inhibitor. There are several spray solutions you can make yourself using a clean spray bottle, including vinegar and water, tea tree oil and water, and hydrogen peroxide. Two to three times a week, spray the grout after a bath or shower with a solution of:
Half-and-half vinegar and water. However, be aware that overuse of vinegar on grout can cause erosion over many years. Water and 15 to 20 drops of tea tree oil. Shake well before each use. Pure hydrogen peroxide in a spray bottle.
Dry the grout after every use. Removing the excess water from tiles and grout after a shower or bath is one of the easiest ways to keep grout looking new. After each use, wipe the shower walls or bath down with an old towel or squeegee.
Keep the bathroom dry. Another great way to keep mold and mildew from growing in your bathroom is by removing the water that allows it to grow. If your bathroom isn’t equipped with an exhaust fan, remove moisture from the air after every shower or bath by opening the window and blowing a stand-up fan out the window.
Seal the grout. Grout should be re-sealed every few years. Sealant can be applied to the grout lines with a paint brush. Allow it to dry, and then remove sealant from the tiles by wiping them in a diagonal direction with a damp cloth or sponge. One applied and cleaned, allow the sealant to cure for about three to four hours.